The overall objective of this project is to study the pathophysiology of acute compartment syndromes by correlating elevated intramuscular pressure variables with short-term and long-term tests of muscle and nerve function. Intramuscular pressure is continuously monitored by the wick technique. Short-term tests will be applied to a human model of acute compartment syndrome, whereas long-term tests will follow pressurization of the canine anterolateral compartment by autologous plasma. Dog studies will determine thresholds of long-term, irreversible myoneural dysfunction after varying amplitudes and durations of intramuscular pressure. Tests of muscle function will include isometric twitch torque, time to peck tension, one-half relaxation time, isometric tetanic torque, and endurance capacity. Functional changes will be correlated with muscle and nerve morphology using light microscopy. External compression of the anterior compartment in human subjects will assess pressure-time thresholds of peroneal nerve dysfunction with elevated intramuscular pressure. Results with this model will be correlated with arterial blood pressures and will be used to determine objectively the best neurological technique for evaluating foot sensibility during an acute, anterior compartment syndrome. In a separate study, the effect of foot and knee position on intramuscular pressures will be determined in patients with tibial fracture. Finally, hyperbaric oxygen will be used to treat impendin and postdecompression acute compartment syndromes in patients. Previous studies of dogs document significant reductions of muscle necrosis and edema with hyperbaric oxygen treatment. Our long-term objective is to improve the diagnosis and management of acute compartment syndromes in patients with normal blood pressures, hypertension, and hypotension (e.g. shock).